# 1 "boot/bootsect.S"
# 1 "<built-in>"
# 1 "<command line>"
# 1 "boot/bootsect.S"
!
! SYS_SIZE is the number of clicks (16 bytes) to be loaded.
! 0x3000 is 0x30000 bytes = 196kB, more than enough for current
! versions of 1
!
SYSSIZE = 0x3000
!
! bootsect.s (C) 1991 Linus Torvalds
!
! bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves
! iself out of the way to address 0x90000, and jumps there.
!
! It then loads 'setup' directly after itself (0x90200), and the system
! at 0x10000, using BIOS interrupts.
!
! NOTE! currently system is at most 8*65536 bytes long. This should be no
! problem, even in the future. I want to keep it simple. This 512 kB
! kernel size should be enough, especially as this doesn't contain the
! buffer cache as in minix
!
! The loader has been made as simple as possible, and continuos
! read errors will result in a unbreakable loop. Reboot by hand. It
! loads pretty fast by getting whole sectors at a time whenever possible.
.code16
.global _start
.text

SETUPLEN = 4 ! nr of setup-sectors
BOOTSEG = 0x07c0 ! original address of boot-sector
INITSEG = 0x9000 ! we move boot here - out of the way
SETUPSEG = 0x9020 ! setup starts here
SYSSEG = 0x1000 ! system loaded at 0x10000 (65536).
ENDSEG = SYSSEG + SYSSIZE ! where to stop loading

! ROOT_DEV: 0x000 - same type of floppy as boot.
! 0x301 - first partition on first drive etc
ROOT_DEV = 0x306

_start:
 mov ax,#BOOTSEG
 mov ds,ax
 mov ax,#INITSEG
 mov es,ax
 mov cx,#256
 sub si,si
 sub di,di
 rep
 movw
 jmpi go,INITSEG
go: mov ax,cs
 mov ds,ax
 mov es,ax
! put stack at 0x9ff00.
 mov ss,ax
 mov sp,#0xFF00 ! arbitrary value >>512

! load the setup-sectors directly after the bootblock.
! Note that 'es' is already set up.

load_setup:
 mov dx,#0x0000 ! drive 0, head 0
 mov cx,#0x0002 ! sector 2, track 0
 mov bx,#0x0200 ! address = 512, in INITSEG
 mov ax,#0x0200+SETUPLEN ! service 2, nr of sectors
 int 0x13 ! read it
 jnc ok_load_setup ! ok - continue
 mov dx,#0x0000
 mov ax,#0x0000 ! reset the diskette
 int 0x13
 j load_setup

ok_load_setup:

! Get disk drive parameters, specifically nr of sectors/track

 mov dl,#0x00
 mov ax,#0x0800 ! AH=8 is get drive parameters
 int 0x13
 mov ch,#0x00
 seg cs
 mov sectors,cx
 mov ax,#INITSEG
 mov es,ax

! Print some inane message

 mov ah,#0x03 ! read cursor pos
 xor bh,bh
 int 0x10

 mov cx,#24
 mov bx,#0x0007 ! page 0, attribute 7 (normal)
 mov bp,#msg1
 mov ax,#0x1301 ! write string, move cursor
 int 0x10

! ok, we've written the message, now
! we want to load the system (at 0x10000)

 mov ax,#SYSSEG
 mov es,ax ! segment of 0x010000
 call read_it
 call kill_motor

! After that we check which root-device to use. If the device is
! defined (!= 0), nothing is done and the given device is used.
! Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending
! on the number of sectors that the BIOS reports currently.

 seg cs
 mov ax,root_dev
 cmp ax,#0
 jne root_defined
 seg cs
 mov bx,sectors
 mov ax,#0x0208 ! /dev/ps0 - 1.2Mb
 cmp bx,#15
 je root_defined
 mov ax,#0x021c ! /dev/PS0 - 1.44Mb
 cmp bx,#18
 je root_defined
undef_root:
 jmp undef_root
root_defined:
 seg cs
 mov root_dev,ax

! after that (everyting loaded), we jump to
! the setup-routine loaded directly after
! the bootblock:

 jmpi 0,SETUPSEG

! This routine loads the system at address 0x10000, making sure
! no 64kB boundaries are crossed. We try to load it as fast as
! possible, loading whole tracks whenever we can.
!
! in: es - starting address segment (normally 0x1000)
!
sread: .word 1+SETUPLEN ! sectors read of current track
head: .word 0 ! current head
track: .word 0 ! current track

read_it:
 mov ax,es
 test ax,#0x0fff
die: jne die ! es must be at 64kB boundary
 xor bx,bx ! bx is starting address within segment
rp_read:
 mov ax,es
 cmp ax,#ENDSEG ! have we loaded all yet?
 jb ok1_read
 ret
ok1_read:
 seg cs
 mov ax,sectors
 sub ax,sread
 mov cx,ax
 shl cx,#9
 add cx,bx
 jnc ok2_read
 je ok2_read
 xor ax,ax
 sub ax,bx
 shr ax,#9
ok2_read:
 call read_track
 mov cx,ax
 add ax,sread
 seg cs
 cmp ax,sectors
 jne ok3_read
 mov ax,#1
 sub ax,head
 jne ok4_read
 inc track
ok4_read:
 mov head,ax
 xor ax,ax
ok3_read:
 mov sread,ax
 shl cx,#9
 add bx,cx
 jnc rp_read
 mov ax,es
 add ax,#0x1000
 mov es,ax
 xor bx,bx
 jmp rp_read

read_track:
 push ax
 push bx
 push cx
 push dx
 mov dx,track
 mov cx,sread
 inc cx
 mov ch,dl
 mov dx,head
 mov dh,dl
 mov dl,#0
 and dx,#0x0100
 mov ah,#2
 int 0x13
 jc bad_rt
 pop dx
 pop cx
 pop bx
 pop ax
 ret
bad_rt: mov ax,#0
 mov dx,#0
 int 0x13
 pop dx
 pop cx
 pop bx
 pop ax
 jmp read_track

!




kill_motor:
 push dx
 mov dx,#0x3f2
 mov al,#0
 outb
 pop dx
 ret

sectors:
 .word 0

msg1:
 .byte 13,10
 .ascii "Loading system ..."
 .byte 13,10,13,10

.org 508
root_dev:
 .word ROOT_DEV
boot_flag:
 .word 0xAA55

.text
endtext:
.data
enddata:
.bss
endbss:
